A developing unit is contained in image forming apparatuses. The developing unit contains powder-type developer or toner. A developing roller is rotatably supported in a body casing of the developing unit. The developing roller is configured to have a cylindrical shape and hold the developer on a circumferential surface thereof. The developing roller is disposed such that a part of the circumferential surface is exposed external to the developing unit across its full length.
The developing unit is configured to develop an electrostatic latent image formed on a circumferential surface of a photosensitive member by facing the circumferential surface of the developing roller and the circumferential surface of the photosensitive member while rotating the developing roller.
A developing unit configured to be received in and removed from a main body of the image forming apparatus (or a developer cartridge) is known. As to the developer cartridge, disclosed are various kinds of configurations to prevent leakage of the developer from a gap between each end portion of the developing roller and the opening during the rotation of the developing roller.
For example, Japanese Laid-Open Patent Publication No. 2001-5287 discloses a developing unit in which side seals are provided to prevent leakage of the developer. The side seals are disposed to slidingly contact both ends of the circumferential surface of the developing roller, thereby preventing the developer from leaking from the gaps between each end of the developing roller and the opening.
Japanese Laid-Open Patent Publication No. 2001-60040 (corresponding to U.S. Pat. Nos. 6356723 B1 and 6496669 B2) discloses a developing cartridge in which safeguard members are provided in addition to the side seals. The safeguard members are disposed on both ends of the opening in which the developing roller is rotatably disposed, with respect to its length. According to this configuration, if a small amount of developer leaks from a sliding portion between each end portion of the developing roller and the side seal, the developer can be received by the safeguard member and thus prevented from leaking outside the developer cartridge.